The present invention generally relates to a ferromagnetic metal type magnetic recording medium and more particularly, to a magnetic recording medium in which performance of a hard carbon film provided, after formation of a magnetic layer, as a protective film for improving practical performance can be maximized.
In ferromagnetic metal type magnetic recording mediums produced by a process in which by a film forming method under vacuum such as vacuum deposition, sputtering, ion plating, etc., Co, Ni or Fe or an alloy mainly consisting of Co, Ni and Fe is formed on a substrate made of polymeric film such as polyester, polyimide, etc. or non-magnetic metal, recording density can be raised remarkably in comparison with known coating type magnetic recording mediums.
Meanwhile, in order to raise recording density, it is prerequisite to minimize not only recording and reproducing defects but spacing loss between a magnetic head and the magnetic recording medium. In addition, the magnetic recording medium is required to have durability. In order to satisfy these requirements, a procedure is known in which after formation of a magnetic layer, a hard amorphous carbon film acting as a protective film and a lubricant layer are provided on the magnetic layer. More concretely, Japanese Patent Laid-Open Publication No. 1-245417 (1989) proposes an arrangement in which a plasma-polymerized film is provided on a ferromagnetic metal thin film prior to formation of a hard carbon film, while Japanese Patent Laid-Open Publication No.3-19122 (1991) discloses that a graphite layer is provided on a ferromagnetic metal thin film. Furthermore, Japanese Patent Laid-Open Publication Nos. 3-83224(1991), 3-116520 (1991), etc. teach that a metallic carbide layer or a metallic layer having discontinuous crystalline structure is provided on a ferromagnetic metal thin film.
However, in the prior art arrangements in which the plasma-polymerized film or the graphite layer is provided on the ferromagnetic metal thin film, it is impossible to obtain excellent adhesive property between the metal thin film and the hard carbon film. As a result, if these known arrangements referred to above are employed in a magnetic tape and a hard disk, durability of the magnetic tape is poor, while the hard disk has such a drawback that the hard carbon film is peeled from the metal thin film.
Meanwhile, in the known arrangements in which the metallic carbide layer or the metallic layer having discontinuous crystalline structure is provided on the ferromagnetic metal thin film, the metal or the metal carbide is sputtered during formation of the hard carbon film so as to be drawn into the hard carbon film and thus, is agglutinated to the magnetic head. In case the known arrangements are employed in a magnetic tape and a hard disk, output of the magnetic tape drops at the time of recording and reproduction, while head crush occurs in the hard disk.